I drove a RHD Alfa on the continent for a number of years and now have a LHD Landy which I drive in the UK for a couple of months a year…
Overtaking – you won't, at least not safely.
Car parks, automated barriers, toll booths – you'll need very long arms or you'll have to get out and walk around each time.
Safety – depends – the Alfa was fine as it had windows in the sides, the Defender is a van and you can only take a left at a T-junction if you hit it at 90 degrees as you can't see anything over your right shoulder. Similarly turning right at roundabouts can be *very* tricky.
In all, If I was living in the UK I would select a RHD.